COMPUTER METHODS FOR ANALYSIS OF RESERVOIR HETEROGENEITY: EXAMPLE FROM A LOWER MISSISSIPPIAN OIL FIELD IN WEST VIRGINIA

Several computational and statistical methods were used in the study of reservoir architec-ture and its relationship to oil production from the Mississippian Big Injun sandstone in Granny Creek field,central West Virginia(USA). Computer programs were written or adapted from published sources to:1)calculate the regression of permeability on porosity;2)map porosity in three dimensions;3)define and map facies inferred from geophysical logs;and 4)estimate origi-nal oil in place,cumulative production,and recovery efficiency. Because regression analysis showed a weak but significant relationship between log and core porosity,and core permeabili-ty,porosity could be used in place of permeability to construct models of the reservoir. Quantita-tive stratigraphic correlation and multidimensional scaling were used to eliminate the effects of structure in the absence of a usable datum. Kriging was used for interpolation between wells, and the results were drawn as cross sections to highlight zones of relatively high porosity. Geo-physical log data and core descriptions were used to define electrofacies by cluster analysis. Esti-mates of original oil in place were combined with cumulative production data to yield estimates of recovery efficiency. Maps of these oil production variables generally showed the same north-south trend observed on lithofacies maps.